Electromagnetic Relays and Selection Specifications
Electromagnetic Relay acts as a electrical switch operated by electromagnet. The coil on the relay forms the electromagnet. When excited by rated voltage, it pulls the moving portion of the relay contacts towards it resulting in electrical contact. Thus it turns a load circuit ON or OFF by energizing an electromagnet, which opens or closes contact in the circuit. A relay has one coil, but may have many contacts. The contact that changes is called pole and the non-moving contacts are called ways. When the coil is off, the contact with pole is called normally closed contact. (NO) The contact established after the coil is energized is called normally open contact. (NC) The coil and the contacts of a relay are electrically galvanically isolated from each other. Relays finds wide use in timers, interlocks circuits, trips and safety units, changeover systems etc. The main parameters required for selection of a relay are, 1. Coil rating 2. Contact rating. 3 Operation ...